This is an R03 application from a new investigator. The goal of this research is to identify the genes and basic mechanisms that are associated with nicotine dependence in humans. Converging evidence suggests that genetic variations in the rate of metabolism of nicotine can play a role in mediating nicotine dependence. The family of CYP450 enzymes, including CYP2A6, CYP2B6 and CYP2D6, play a pivotal role in nicotine metabolism. While genetic variation in the CYP2A6 gene has been shown to affect nicotine metabolism and alter an individuals' smoking behavior, the effects of genetic variation in CYP2B6 and CYP2D6 on nicotine metabolism and dependence remain to be elucidated. Thus, in the research outlined in this application, we will assess whether there is a correlation between CYP2B6 and/or CYP2D6 genotypes and specific nicotine pharmacokinetic parameters. We will concentrate on four specific phenotypes, which have shown the highest heritabilities in previous in vivo nicotine pharmacokinetics studies: (i) nicotine and cotinine half-life, (ii) nicotine clearance, (iii) cotinine volume of distribution and (iv) rate constant marking CYP450 activity. We will also evaluate whether the CYP2B6 and CYP2D6 genotypes modulate the effect of the CYP2A6 genotype on nicotine pharmaeokinctic parameters and will estimate the proportion of the variation in nicotine metabolism that is explained by each of these three genes and by any gene-gene interactions between them. Dr. Huijun Ring, along with Drs. Neal Benowitz, Gary Swan, Rachel Tyndale and Ana Valdes, form a strong multi-disciplinary research team that uniquely qualifies them to carry out the proposed research. The proposed research will be the first to completely characterize the genotypes of all three nicotine C-oxidase genes and to study their relative roles in in vivo nicotine metabolism. This project is an important pilot study to explore the relationship between CYP450 polymorphisms and nicotine metabolism, and we intend to follow it up with future studies that have larger sample size in order to test for more nicotine addiction related phenotypes. This systematic genetic approach will help to identify genetic mechanisms that underlie individual susceptibility to nicotine dependence and provide new insights into the etiology of smoking and will facilitate the development of new intervention and preventive strategies.